1. Field of the Invention
The present invention relates to a technology for removing a foreign substance, such as dust, adhering to a surface of an optical member provided on an optical axis of an optical apparatus, such as an imaging apparatus.
2. Description of the Related Art
In imaging apparatuses, such as digital cameras, which perform imaging of a subject by converting a subject image into an electrical signal, an imaging light-beam is received by an image sensor. Then, a photoelectric conversion signal output from the image sensor is converted into image data. The image data is recorded on a recording medium, such as a memory card. A charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) sensor can be used as the image sensor.
In such imaging apparatuses, an optical low-pass filter or an infrared cut filter is disposed on a subject side of the image sensor. When foreign substances, such as dust, adhere to the surfaces of the filter, the foreign substances produce black spots in a captured image. Consequently, visual quality of the image deteriorates.
In particular, in digital single-lens reflex cameras with interchangeable lenses, mechanical operating units, such as a shutter and a quick-return mirror, are disposed in vicinity of an image sensor. Sometimes, foreign substances, such as dust, are generated by the operating units and adhere to the surface of the image sensor or the filter. In addition, when the lens is changed, a foreign substance, such as dust, may enter the camera body from an opening of a lens mount and may adhere to the surface of the image sensor or the filter.
In order to avoid such phenomena, U.S. Pat. No. 7,324,148 discusses a technology for providing a dust-proof screen, which transmits an imaging light-beam, on a subject side of an image sensor, and for vibrating the dust-proof screen using a piezoelectric element to remove a foreign substance, such as dust, adhering to the surface of the dust-proof screen.
According to the technology discussed in U.S. Pat. No. 7,324,148, a voltage is applied to an electronic element joined to a dust-proof screen so as to remove a foreign substance adhering to the dust-proof screen. Then, the piezoelectric element is driven to displace the dust-proof screen in an optical-axis direction. Thus, screen vibrations are caused. In such a configuration, a space between the dust-proof screen and the image sensor is sealed with an elastic member, such as a rubber member. However, sometimes, attenuation of vibrations of the elastic member varies with the temperature of the vicinity of the dust-proof screen, so that an amplitude of the vibration of the dust-proof film changes.
When a user cleans directly the dust-proof screen using a cotton swab or lens cleaning paper, the dust-proof screen may be scratched. The failure probability of the dust-proof screen is increased according to the number of times of cleaning. Thus, unless the amplitude of vibration of the dust-proof screen during a foreign-substance removal operation is reduced with an increase in the number of times of cleaning thereof, there is a fear of breakage of the dust-proof screen.
A method of providing an electric circuit for applying a voltage to a piezoelectric element with a circuit capable of applying an appropriate voltage according to the temperature at driving thereof and the number of times of cleaning has been considered to solve such a problem. However, a plurality of step-up circuits and resistors are required to generate different voltages. This is a cause for increasing the cost and size of a digital single-lens reflex camera.